1. Field of the Invention
The present invention relates to an ink jet printer head for a printer and more particularly to the ink jet print head using thermal energy to eject ink droplets from a plurality of nozzles so that the ink droplets impinge on a print sheet.
2. Description of the Related Art
Thermal-pulse ink jet printers have been described in, among other sources, Japanese Patent Application Kokai Nos. SHO-48-9622 and SHO-54-51837. In one type of thermal-pulse ink jet printer, a print head provided thereto includes a plurality of ink droplet generators. Each ink droplet generator includes an ink chamber filled with ink, a thermal resistor formed to the wall of the ink chamber, and a nozzle formed in the wall of the ink chamber. The nozzle fluidly connects the ink chamber with the atmosphere. Pulses of voltage are selectively applied to the thermal resistors of the plurality of ink droplet generators so that an energized thermal resistor generates a pulse of heat. The pulse of heat generated at an energized thermal resistor rapidly vaporizes a small amount of the ink filling the ink chamber. The force produced by the expansion of the resultant vapor bubble ejects an ink droplet from the corresponding nozzle. The vapor bubble then collapses and disappears.
Concrete examples of thermal resistors for use in thermal-pulse ink jet printers have been described in a presentation made at the Feb. 26, 1992 convention for High Technology for Hard Copy sponsored by the Japan Technology Transfer Association, on page 58 of the Dec. 28, 1992 edition of Nikkei Mechanical and in the August 1988 edition of Hewlett-Packard-Journal. As is shown in FIG. 1, a typical thermal resistor used in a print head of a thermal-pulse ink jet printer includes a thin-film resistor 443 and a thin film conductor 444, both covered with an anti-oxidation layer 445. An anti-cavitation layer 446 is formed over a heating area of the anti-oxidation layer 445 for preventing cavitation of the anti-oxidation layer 445. An additional anti-cavitation layer 447 can also be provided.
Copending U.S. patent application Ser. No. 068,348 (not prior art) describes a thermal resistor formed from a Cr--Si--SiO or Ta--Si--SiO alloy thin-film resistor and a nickel thin-film conductor. The excellent anti-pulse, anti-oxidation, anti-cavitation, and anti-corrosion properties of these materials allows forming the thermal resistor without the anti-oxidation layer or the anti-cavitation layers. Because the ink comes into direct contact with this thermal resistor, the pulse of heat produced thereby is transferred to the ink with 30 to 60 time greater efficiency. Vaporization and ejection of ink is therefore greatly improved.
Another copending U.S. patent application Ser. No. 172,825 (not prior art) describes an on-demand type print head incorporating the above-described protection-layerless thermal resistors. Because transfer of heat is so efficient when using the protection-layerless thermal resistors, vapor bubbles can be generated by applying only a small voltage to the thermal resistors. Therefore, the area around the thermal resistors remains cool enough to allow forming a print head that includes a large-scale integrated circuit, for driving the print head, adjacent to the thermal resistors.
In order to allow printing over the entire surface of a sheet to be printed on, ink jet printers usually are provided with a carriage for supporting the print head and a platen roller for supporting the sheet adjacent to the print head. The carriage is provided to a slider so as to be returnably scanningly movable in a main scanning direction. The platen roller is provided so as to be capable of step feeding the sheet supported therein in an auxiliary scanning direction perpendicular to the main scanning direction. Because the print head can be scanned widthwise across the surface of the sheet in the main scanning direction and because the sheet can be step fed in the auxiliary direction, the entire surface of the sheet can be printed on.
It has been desired to produce a print head with a length equal to the width of the sheet to be printed on. With such a long print head, termed a line head, an entire line of a sheet could be printed without scanning the head across the sheet. Printing could be performed faster and without a complicated drive being required for synchronizing the main scanning operation with the auxiliary scanning operation.